Process of producing acetic acid



Patented Aug. 21, 1928.

UNITED STATES FRANCIS GEORGE RAWLING, OF MADISON, WISCONSIN.

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No Drawing.

This invention relates to the production of acetic acid from wood and pertains to a particular process whereby wood is treated chemically to produce the desired acld yield- 6 ing material while conserving the wood as such and only slightly modified from its original condition.

One feature of the invention is the extraction of acetic acid and acetates from 10 wood by subjecting the wood to the action of chemical materials in aqueous solutlon at elevated temperatures and pressures.

Heretofore, in the production of acetic acid from wood, it has been customary to employ l5 methods of dry distillation, resulting in the destruction of the wood and leaving the latter as a carbonized residue of low value having little use .as a substitue for wood. The present improvement provides a process whereby the wood residues, after the removal of acetic acid, are only slightly altered from the condition of, the wood at' the time of initial treatment. 'As contrasted to the previous carbonized residues, the present inven 2 tion provides for wood-residues, wh1ch may i be used as substitutes for fresh wood in the manufacture of methyl alcohol, ethyl alcohol, pulp, aper and paper products, cellulose andce lulose products and the like, by present known processes.

The several steps of the process of the resent invention will now be described. nitially, wood is cut into pieces of convenient size and impregnated with or without 85 the application 0 vacuum or pressure, or of pressure applied subsequent to the vacuum,

in a suitable vesselwith an aqueous solution containing sodium sulphite and an alkali or a substance or substances capable of pro- 40- 'ducing an alkali either'by hydrolysis or under the conditions of heating to be described, for example, sodium bicarbonate, trisodium phosphate, or sodium sesquicarbonate. A definition which will include sodium bicarbonate and sodium. carbonate and salts of suitable alkalinity will be satisfied by the term sodi um salts of weakly ionized polybasic acids, which salts, in

unimolar solution inwater have a P numher. between 11 and 7.- Such a definlt on excludes sodium sulphide and caustic soda. For example, small pieces of wood maybe impregnatedlwith an aqueous solution coni taining four percent of sodium sulphite and "six percentoisqditlm carbonate. The wood may be steamed before treatment with the with other salts and organic material.

Application filed February 12, 1926. Serial No. 87,951.

chemical solution to assist the impregnation, depending on the condition of the wood. The amount of sodium sulphite to be absorbed by the wood should not be in excess of twenty pounds for each hunded pounds of wood. The sodium sulphites assist in the action by dissolving the lignin and introducing a large amount of undesirable or game material into the 'llquld. Since an excess of alkali will also decomposethe ligno-- 'celluloses by dissolving the lignin and thus introducing undesirable organic material into the solution, such excess is to be avoided. 5

To the solution of sulphite and alkali unabsorbed by the wood is w'ithdrawn from the digesting vessel as far as practicable after a period of time, usually one hour is sufficient, and thereafter the digest'or and its contained impregnated Wood is heated to a temperature of at least 110 C. and not over 160 C. fora suitable period of time, usually not more than six hours. The heating is preferably accomplished by admission of steam. During the heating action, the pressure in the vessel may rise as high as 150 pounds per square inch and the pressure ,may be releasedpartially from time to time,

if found necessary. After the completion of the heating, the contents of the vessel may be removed either under pressure or after the pressure has been released.

The liquid is separated from the solid residue and the latter maybe subjected to furthertreatment by known methods in the manufacture of methyl alcohol, ethyl alcohol, pulp, paper, paper products, cellulose and cellulose products, and the like. The liquid contains acetates in solution, together The solid residue is not greatly changed in appearance from the original wood, and it is not pulped by the heating process.

The separated liquid is rendered acid-by the addition of any suitable acid-or acid salt, such as nitre cake'or sulphuric acid. The acid liquid is then boiled and the acetic acidcis set free and distils off together with water and sulphur dioxide. The vapors are condensed, forming an aqueous solution consisting principally of acetic acid and sulphurous acid. The separated liquid may be treated in a second manner, by making it alkaline by the addition of calcium hydroxide, or lime or other metallic hydroxide, carbonate or bicarbonate. the corresponding sulphite of which is insoluble in water and the corresponding acetate of which soluble. In this manner, the sulphites present in the separated liquor are precipitated. The liquid after this treatment is separated from the solids present, and is made acid with the addition of a suitable acid or acid salt, preferably sulphuric acid or nitre cake and boiled. The acetic acid is set free and distils, together with water and a small amount of sulphur dioxide. The vapors are condensed, forming an aqueous solution consisting principally of acetic acid and a trace of sulphurous acid...

The condensate from the two methods outlined above can be converted into an aqueous solution of calcium acetate by treatment with lime or calcium carbonate,or into other acetates by neutralizingthe solution with the appropriate base, either as bydroxide or carbonate, for example,- such bases as lead, magnesium or barium, from which acetic acid and other acetates may be prepared by known methods.

I claim:

1. The process of preparing acetic acid by extraction from wood, which process comprises impregnating wood'with a treating material consisting of an aqueous solu-.

' tion of a mixture of sodium sulphite and an alkali, the strength of said treating material being capable of neutralizing acetic acid from the wood but not sufficient to materially aifect the lignin content of the wood,

subjecting the wood and said treating material to a heat treatment of at least 110 C. and not over 160 C. and thereby forming acetates in solution, rendering the material of the solution acid, and recovering acetic acid from the solution.

2. The process of preparing acetic acid by extraction from wood, which process comprises impregnating wood with an aqueous solution of sodium sulphite and an alkali, the strength of said aqueous solution being capable of neutralizing acetic acid from the wood but not suflicient to materially affect the lignin content of the wood, digesting the wood and the treating materialand thereby forming acetates in solution, rendering the material of the solution acid, and recovering the acetic acid from the solution,

3. The process of preparing acetic acid by extraction from wood, which process comprises impregnating wood with a treatin material consisting of an aqueous solution 0 a mixture of sodium sulphite and an alkali, v

the strength of said aqueous solution being capable of=neutralizing acetic acid from the wood but not suflicient to materially affect the lignin content of the wood, subjecting the wood and said treating material to a heat 'treatment of at least 110 C. and not over material including an aqueous solution of a mixture of sodium sulphite and a salt capable of producing alkali by hydrolysis and which salt in unimolar solution in water has a P number between 11 and 7, subjecting the Wood in said treating material to a digesting treatment at a temperature of at least 110 C. and not over 160 (1., and thereby forming acetates in solution, stopping the digesting action before the wood is pulped, separating the solution from the wood rendering the solution acid, heating the solution and distilling ofi acetic acid from the solution.

5. The process of preparing acetic acid by extraction from wood, which process comprises impregnating wood with a treating material including an aqueous solution of a mixture of sodium sulphite and a soluble carbonate, subjecting the wood in said treating material to a digesting treatment at a temperature of at least 110 C. and not over 160 C., and thereby forming acetates in solution, stopping the digesting action before the wood is pulped, separating the solution from the wood rendering the solution acid, heating the solution and distilling off acetic acid from the solution.

6. The process of preparin acetic acid by extraction from wood, w ich process comprises impregnating wood with a treating material including an aqueous solution of a mixture of sodium sulphite and sodium carbonate, subjecting the wood in said treating material to a digesting treatment at a temperature of at least 110 C. and-not over 160 0., and thereby forming acetates ,in' solution, stopping the digesting action before the wood is pulped, separating the solution from the wood rendering the solution acid, heating the solution and distilling ofi acetic acid from. the solution.

7. In the process of preparing acetic acid by treatment of Wood, the steps comprising digesting wood with a solution consisting of sodium sulphite and an alkali and thereby forming acetates, and thereafter producing acetic acid from said acetates, the strength a by treatment of wood, the steps comprising I digesting wood'with a solution consisting of ium sulphite and an alkali and at a temperature of at least 110 C. and not over 160 C. and thereby forming acetates, and thereafter producing acetic acid from said acetates. 4

9. The process of preparing acetic acid by extraction from wood, which process comprises impregnating wood with an aqu us solution of sodium sulphite and the sodgm salt of a weakly ionized polyba'sic acid and which salt in unimolar solutionin water has a P number between 11 and 7,

digesting the wood and the treating material and thereby forming acetates in solution, rendering the material of the solution acid and recovering acetic acid from the solution. In testimony whereof I afiix my signature.

FRANCIS G. RAWLING. 

